The present invention relates generally to methods of applying protective films to electronic device surfaces and to devices comprising protective films.
Protective films are used to cover and protect a variety of materials and devices from, for example, scratches or dents that may be imparted during transport or use of the device. Protective films may be used to protect, for example, the surface of digital electronic device components during manufacture, or may be adhered to a completed device to protect it from damage during normal day-to-day use. A variety of protective films are known, each having properties that may be advantageous for some uses and disadvantageous for other uses. One form of protective film used in the art is coated on one side with a layer of a dry pressure-sensitive adhesive that has sufficient tack to form a secure contact with the device while permitting slight repositioning of the film after adherence. Protective films are often transparent, and may permit the use of touch-sensitive features of the electronic device through the film.
Typically, when a dry protective film, particularly a protective film having an adhesive layer, is applied to a surface, air is easily trapped between a device surface and the film during application, causing the appearance of bubbles. Bubbles are undesirable for aesthetic reasons but also because their presence over an optical screen distorts images on a screen viewed by a device user. Prior methods of eliminating trapped air bubbles beneath protective films utilize an aqueous solution or other solvent to temporarily reduce adherence between a film and a device, permitting trapped air to be forced out by mechanical pressure. Known methods, for example, include spraying a protective film (or device surface) with water or another liquid, applying the wet film to the device surface to be protected (or applying the film to the wet device surface), and using pressure (e.g., with a squeegee) to smooth the film and force out any trapped air bubbles. In doing so, the water or other liquid is also forced out from between the film and the device surface, and collects at an edge of the film.
Thus, prior methods required introduction of a liquid to the outer surface of a device, requiring a user to take additional steps to remove liquid after a film is applied to a device. A significant disadvantage to using a wet solution to apply a protective film is potential introduction of liquid into an electronic device, for example, through the apertures for the speaker or head set jack. In some cases, liquid entering an interior housing of a device may cause a device to fail. For this reason, device manufacturers commonly include moisture sensitive indicators within their devices to help diagnose device failure. In some cases, a manufacturer will void a device's warranty where inspection of a device and its moisture indicators show exposure to moisture.
Another drawback of many protective films is the high visibility of fingerprints, smudges or other marks on the film, resulting, for example, from handling of a device. In particular, visibility of fingerprints or other marks on films covering electronic device bodies or display screens is aesthetically and functionally undesirable. A visible residue over a display screen, for example, may distort the transmission of light from the screen resulting in distortion of an image viewed on the screen. Matte surface treatments have been used to address this problem, but the application of typical matte surfaces over an optical screen reduces optical transmission.